System and method for an adjusting optical proximity effect for an exposure apparatus

ABSTRACT

A method for matching a first OPE curve ( 700 ) for a first exposure apparatus ( 10 A) used to transfer an image to a wafer ( 28 ) to a second OPE curve ( 702 ) of a second exposure apparatus ( 10 B). The method can include the step of adjusting a tilt of a wafer stage ( 50 ) that retains the wafer to adjust the first OPE curve. As provided herein, the first exposure apparatus ( 10 A) has the first OPE curve ( 700 ) because of the design of the components used in the first exposure apparatus ( 10 A), and the second exposure apparatus ( 10 B) has a second OPE curve ( 702 ) because of the design of the components used in the second exposure apparatus ( 10 B). Further, the tilt of the wafer stage ( 50 ) can be selectively adjusted until the first OPE curve ( 700 ) approximately matches the second OPE curve ( 702 ). With this design, the two exposure apparatuses ( 10 A) ( 10 B) can be used for the same lithographic process. Stated in another fashion, exposure apparatuses ( 10 A) ( 10 B) from different manufacturers, when using the same reticle ( 26 ), will transfer similar images to the wafer ( 28 ).

RELATED INVENTIONS

This application claims priority on U.S. Provisional Application Ser.No. 61/030934, filed Feb. 22, 2008 and entitled “Scanner-To-Scanner OPEMatching”. As far as permitted, the contents of U.S. ProvisionalApplication Ser. No. 61/030934 are incorporated herein by reference.

BACKGROUND

Exposure apparatuses for semiconductor processing are commonly used totransfer images from a reticle onto a semiconductor wafer duringsemiconductor processing. A typical exposure apparatus includes (i) anillumination system having an illumination source and an illuminationoptical assembly, (i) a reticle stage assembly that positions a reticle,(iii) a projection optical assembly, and (iv) a wafer stage assemblythat positions a semiconductor wafer. With this design, the illuminationsystem illuminates the reticle to transfer images to the wafer.

Lithographers commonly desire to use exposure apparatuses from differentmanufacturers for the same lithographic process. Unfortunately, exposureapparatuses from different manufacturers exhibit different behavior inoptical proximity effects (“OPE”). This can be caused by the unavoidabledifferences in (i) the illumination sources, (ii) the illuminationoptical assemblies, (iii) the projection optical assemblies, and/or (iv)the synchronization between the reticle stage assembly and the waferstage assembly. As a result thereof, exposure apparatuses from differentmanufacturers, when using the same reticle, will transfer differentimages to the wafer. Thus, the exposure apparatuses from differentmanufacturers are not interchangeable.

SUMMARY

The present invention is directed to a method for matching a first OPEcurve for a first exposure apparatus used to transfer an image to awafer to a second OPE curve of a second exposure apparatus. The methodincludes the step of adjusting a tilt of a wafer stage that retains thewafer to adjust the first OPE curve. As an overview, the first exposureapparatus has the first OPE curve because of the design of thecomponents used in the first exposure apparatus, and the second exposureapparatus has a second OPE curve because of the design of the componentsused in the second exposure apparatus. Further, as provided herein, thetilt of the wafer stage can be selectively adjusted until the first OPEcurve approximately matches the second OPE curve. With this design, thetwo exposure apparatuses can be used for the same lithographic process.Stated in another fashion, exposure apparatuses from differentmanufacturers, when using the same reticle, will transfer similar imagesto a wafer.

As used herein, the term optical proximity effects (“OPE”) shall meanthe unavoidable differences in width, also known as critical dimension(“CD”) of images of features that have the same width on the reticle dueto differing proximity of one feature to its neighbor, where thedistance from the center of one image to its nearest neighbor isreferred to as “pitch”. Further, the term “OPE curve” shall mean a graphof image CD vs. pitch for features of similar CD but different pitches.Moreover, as used herein, the term “approximately matches” shall meanthat the CDs through pitch of the first exposure apparatus are as closeas possible to the CDs through pitch of the second exposure apparatus.For example, with certain non-exclusive designs, the first OPE curveapproximately matches the second OPE curve when an RMS difference of theCD through pitch of the first exposure apparatus when compared to the CDthrough pitch of the second exposure apparatus is approximately fivenanometers or less. In another non-exclusive design, the first OPE curveapproximately matches the second OPE curve when an RMS difference of theCD through pitch of the first exposure apparatus when compared to the CDthrough pitch of the second exposure apparatus is approximately twonanometers or less.

In one embodiment, the method includes the step of lithographic modelingto estimate the first OPE curve of the first exposure apparatus with thewafer stage at a plurality of alternative adjustment angles. With thisdesign, the matching process can be done without test exposures to thewafer. This reduces the cost of matching the exposure apparatuses.

Additionally, the present invention can further include at least one ormore of the steps of: (i) adjusting a numerical aperture (NA) of aprojection optical assembly of the first exposure apparatus to adjustthe first OPE curve; (ii) adjusting a numerical aperture of anillumination system of the first exposure apparatus to adjust the firstOPE curve; (iii) adjusting a wavelength spectrum of an illuminationsystem of the first exposure apparatus to adjust the first OPE curve;(iv) adjusting an annular ratio of an illumination system of the firstexposure apparatus to adjust the first OPE curve; and (v) adjusting ascan synchronization of a reticle stage and the wafer stage of the firstexposure apparatus to adjust the first OPE.

Moreover, the present invention is direct to a method of making a waferthat includes the steps of providing a substrate, matching the first OPEcurve to the second OPE curve and forming an image on the substrate withthe first exposure apparatus.

In another embodiment, the present invention comprises the steps of (i)retaining the wafer with a wafer stage, the wafer stage being tiltableabout a first tilting axis; (ii) estimating the first OPE curve withlithographic modeling of the first exposure apparatus with the waferstage at a plurality of alternative adjustment angles; and (iii)adjusting a tilt of a wafer stage that retains the wafer to adjust thefirst OPE curve until the first OPE curve approximately matches thesecond OPE curve.

The present invention is also direct to a first exposure apparatus fortransferring an image to a wafer, the first exposure apparatus having aninitial first OPE curve that is different than a second OPE curve of asecond exposure apparatus. In one embodiment, the first exposureapparatus includes (i) a wafer stage that retains the wafer; (ii) awafer stage mover for moving the wafer stage and the wafer along a scanaxis and about a tilting axis that is orthogonal to the scan axis; and(iii) an OPE adjuster that controls the wafer stage mover to rotate thewafer stage and the wafer about the tilting axis to adjust the initialfirst OPE curve of the first exposure apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1 is a schematic illustration of an assembly having features of thepresent invention;

FIG. 2 is a simplified side view of a portion of a wafer stage havingfeatures of the present invention, a wafer, and a plurality of aerialimages;

FIGS. 3A and 3B are simplified illustrations of an illumination patternwith different sigmas, where “sigma” is the ratio of illuminationapparatus NA to projection lens NA;

FIGS. 4A and 4B are simplified illustrations of a pupil fill withdifferent numerical apertures;

FIGS. 5A and 5B are simplified illustrations of alternative laserspectra and the resulting aerial images;

FIG. 6 is a flow chart that illustrates one embodiment of a processhaving features of the present invention;

FIG. 7 is a simplified graph that illustrates an OPE for alternativeexposure apparatuses;

FIG. 8 is a simplified graph that illustrates a difference between OPE'sof alternative exposure apparatuses;

FIG. 9A is a flow chart that outlines a process for manufacturing adevice in accordance with the present invention; and

FIG. 9B is a flow chart that outlines device processing in more detail.

DESCRIPTION

FIG. 1 is a schematic illustration of a precision assembly, thatincludes a first exposure apparatus 10A having features of the presentinvention and a second exposure apparatus 10B. The design of thecomponents of each exposure apparatus 10A, 10B can be varied pursuant tothe teachings provided herein. As illustrated in FIG. 1, the exposureapparatuses 10A, 10B can be somewhat similar in design. Alternatively,the exposure apparatuses 10A, 10B can be quite different. For example,the exposure apparatuses 10A, 10B can be made by differentmanufacturers.

In one embodiment, each exposure apparatus 10A, 10B includes anapparatus frame 12, an illumination system 14 (irradiation apparatus), aprojection optical assembly 16, a reticle stage assembly 18, a waferstage assembly 20, a measurement system 22, and a control system 24.Further, the first exposure apparatus 10A includes an OPE adjuster 25that selective adjusts the OPE for the first exposure apparatus 10A.

As an overview, the first exposure apparatus 10A has a first OPE curve700 (illustrated in FIG. 7) because of the design of the components usedin the first exposure apparatus 10A, and the second exposure apparatus10B has a second OPE curve 702 (illustrated in FIG. 7) because of thedesign of the components used in the second exposure apparatus 10A.Further, as provided herein, the OPE adjuster 25 can be used toselectively adjust the first OPE curve 700 of the first exposureapparatus 10A so that the first exposure apparatus 10A has an adjustedOPE curve 704 (illustrated in FIG. 7). As a result thereof, the OPEadjuster 25 can be manipulated until the adjusted OPE curve 704 of thefirst exposure apparatus 10A approaches and is relatively close to thesecond OPE curve 702 of the second exposure apparatus 10B. Stated inanother fashion, the OPE adjuster 25 can be manipulated until theadjusted OPE curve 704 of the first exposure apparatus 10A matches thesecond OPE curve 702 of the second exposure apparatus 10B. With thisdesign, the two exposure apparatuses 10A, 10B can be used for the samelithographic process. Stated in another fashion, exposure apparatuses10A, 10B from different manufacturers, when using the same reticle 26,will transfer similar images to a wafer 28.

A number of Figures include an orientation system that illustrates an Xaxis, a Y axis that is orthogonal to the X axis and a Z axis that isorthogonal to the X and Y axes. It should be noted that any of theseaxes can also be referred to as the first, second, and/or third axes.

The exposure apparatuses 10A, 10B are particularly useful as alithographic device that transfers a pattern (not shown) of anintegrated circuit from the reticle 26 onto the semiconductor wafer 28.The exposure apparatuses 10A, 10B mount to a mounting base 30, e.g., theground, a base, or floor or some other supporting structure.

There are a number of different types of lithographic devices. Forexample, the exposure apparatuses 10A, 10B can be a step-and-scan typephotolithography system that exposes the wafer 28 while the reticle 26and the wafer 28 are stationary. In the step and scan process, the wafer28 is in a constant position relative to the reticle 26 and theprojection optical assembly 16 during the exposure of an individualfield. Subsequently, between consecutive exposure steps, the wafer 28 isconsecutively moved along a scan axis 31A (e.g. the Y axis in FIG. 1)with the wafer stage assembly 20 perpendicularly to an optical axis 31 B(e.g. the Z axis in FIG. 1) of the optical assembly 16 so that the nextfield of the wafer 28 is brought into position relative to theprojection optical assembly 16 and the reticle 26 for exposure.Following this process, the images on the reticle 26 are sequentiallyexposed onto the fields of the wafer 28, and then the next field of thewafer 28 is brought into position relative to the optical assembly 16and the reticle 26.

However, the use of the exposure apparatuses 10A, 10B provided hereinare not limited to a photolithography system for semiconductormanufacturing. The exposure apparatuses 10A, 10B, for example, can beused as an LCD photolithography system that exposes a liquid crystaldisplay device pattern onto a rectangular glass plate or aphotolithography system for manufacturing a thin film magnetic head.

The apparatus frame 12 is rigid and supports the components of therespective exposure apparatus 10A, 10B. The apparatus frame 12illustrated in FIG. 1 supports the reticle stage assembly 18, theoptical assembly 16 and the illumination system 14 for the respectiveexposure apparatus 10A, 10B above the mounting base 30.

The illumination system 14 includes an illumination source 32 and anillumination optical assembly 34. The illumination source 32 emits abeam (irradiation) of light energy. The illumination optical assembly 34guides the beam of light energy from the illumination source 32 to thereticle 26. The beam illuminates selectively different portions of thereticle 26 and exposes the wafer 28. In FIG. 1, the illumination source32 is illustrated as being supported above the reticle stage assembly18. However, the illumination source 32 can be secured to one of thesides of the apparatus frame 12 and the energy beam from theillumination source 32 can be directed to above the reticle stageassembly 18 with the illumination optical assembly 34.

The illumination source 32 can be a g-line source (436 nm), an i-linesource (365 nm), a KrF excimer laser (248 nm), an ArF excimer laser (193nm) or a F₂ laser (157 nm). Alternatively, the illumination source 32can generate beams such as an extreme ultraviolet or x-ray beams.

In certain embodiments, the illumination optical assembly 34 of thefirst exposure apparatus 10A can include one or more lenses 36(illustrated as boxes in phantom) that can be selectively moved by alens mover 38 (illustrated as a box in phantom) to adjust a sigma of theillumination system 14.

The projection optical assembly 16 projects and/or focuses the lightfrom the reticle 26 to the wafer 28. Depending upon the design of theexposure apparatuses 10A, 10B, the projection optical assembly 16 canmagnify or reduce the image illuminated on the reticle 26. It could alsobe a 1× system.

In certain embodiments, the projection optical assembly 16 of the firstexposure apparatus 10A can include a plate 40 (illustrated as a box inphantom) having an aperture 42 (illustrated as a box in phantom) with asize that is adjustable with an aperture mover 44 (illustrated as a boxin phantom) to selectively adjust a numerical aperture of the projectionoptical assembly 16.

The reticle stage assembly 18 holds and positions the reticle 26relative to the projection optical assembly 16 and the wafer 28. Thereticle stage assembly 18 can include a reticle stage 46, and a reticlestage mover 48. The size, shape, and design of each these components canbe varied. The reticle stage 46 retains the reticle 26 and can include achuck (not shown) for holding the reticle 26.

The reticle stage mover 48 moves and positions the reticle stage 46. Forexample, the reticle stage mover 48 can move the reticle stage 46 andthe reticle 26 along the Y axis, along the X axis, and about the Z axis.Alternatively, for example, the reticle stage mover 48 for one or bothof the exposure apparatuses 10A, 10B could be designed to move thereticle stage 46 and the reticle 26 with more than three degrees offreedom, or less than three degrees of freedom. For example, the reticlestage mover 48 can include one or more linear motors, rotary motors,planar motors, voice coil actuators, or other type of actuators.

Somewhat similarly, the wafer stage assembly 20 holds and positions thewafer 28 with respect to the projected image of the illuminated portionsof the reticle 26. The wafer stage assembly 20 can include a wafer stage50, and a wafer stage mover 52. The size, shape, and design of eachthese components can be varied. The wafer stage 50 retains the wafer 28and can include a chuck (not shown) for holding the wafer 28.

The wafer stage mover 52 moves and positions the wafer stage 50. Forexample, the wafer stage mover 52 can move the wafer stage 50 and thewafer 28 along the X, Y and Z axes, and about the X, Y and Z axes.Alternatively, for example, the wafer stage mover 52 for one or both ofthe exposure apparatuses 10A, 10B could be designed to move the waferstage 50 and the wafer 28 with less than six degrees of freedom. Forexample, the wafer stage mover 52 can include one or more linear motors,rotary motors, planar motors, voice coil actuators, or other type ofactuators.

Further, in photolithography systems, when linear motors (see U.S. Pat.Nos. 5,623,853 or 5,528,118) are used in a wafer stage or a mask stage,the linear motors can be either an air levitation type employing airbearings or a magnetic levitation type using Lorentz force or reactanceforce. Additionally, the stage could move along a guide, or it could bea guideless type stage that uses no guide. As far as is permitted, thedisclosures in U.S. Pat. Nos. 5,623,853 and 5,528,118 are incorporatedherein by reference.

Alternatively, one of the stages could be driven by a planar motor,which drives the stage by an electromagnetic force generated by a magnetunit having two-dimensionally arranged magnets and an armature coil unithaving two-dimensionally arranged coils in facing positions. With thistype of driving system, either the magnet unit or the armature coil unitis connected to the stage and the other unit is mounted on the movingplane side of the stage.

Movement of the stages as described above generates reaction forces thatcan affect performance of the photolithography system. Reaction forcesgenerated by the wafer (substrate) stage motion can be mechanicallytransferred to the floor (ground) by use of a frame member as describedin U.S. Pat. No. 5,528,100 and published Japanese Patent ApplicationDisclosure No. 8-136475. Additionally, reaction forces generated by thereticle (mask) stage motion can be mechanically transferred to the floor(ground) by use of a frame member as described in U.S. Pat. No.5,874,820 and published Japanese Patent Application Disclosure No.8-330224. As far as is permitted, the disclosures in U.S. Pat. Nos.5,528,100 and 5,874,820 and Japanese Patent Application Disclosure No.8-330224 are incorporated herein by reference.

For each exposure apparatus 10A, 10B, the measurement system 22 monitorsmovement of the reticle 26 and the wafer 28 relative to the opticalassembly 16 or some other reference. With this information, the controlsystem 24 can control the reticle stage assembly 18 to preciselyposition the reticle 26 and the wafer stage assembly 20 to preciselyposition the wafer 28. For example, the measurement system 22 canutilize multiple laser interferometers, encoders, and/or other measuringdevices.

For each exposure apparatus 10A, 10B, the control system 24 is connectedto the reticle stage assembly 18, the wafer stage assembly 20, and themeasurement system 22. The control system 24 receives information fromthe measurement system 22 and controls the stage mover assemblies 18, 20to precisely position the reticle 26 and the wafer 28. Further, incertain embodiments, the control system 24 can control the illuminationsource 32 to adjust the illumination beam, the lens mover 38 to adjustthe sigma, and/or the aperture mover 44 to adjust the numericalaperture. The control system 24 can include one or more processors andcircuits.

The OPE adjuster 25 is used to precisely adjust the OPE of the firstexposure apparatus 10A to enable precise matching of OPE effects due tolaser-bandwidth differences, scan-synchronization differences, andsimilar effects that are difficult to compensate for directly. In FIG.1, the OPE adjuster 25 is electrically connected to the control system24 of the first exposure apparatus 10A. Alternatively, for example, theOPE adjuster 25 can be directly integrated into the control system 24.

In one embodiment, the OPE adjuster 25 includes one or more controlswitches 54 that can be controlled by a user to selectively vary thetool parameters of the first exposure apparatus 10A to selectivelyadjust the adjusted OPE 704. For example, in FIG. 1, the OPE adjuster 25includes three separate control switches 54. Alternatively, the OPEadjuster 25 can include more than three or fewer than three separatecontrol switches 54.

Moreover, in FIG. 1, each control switch 54 is illustrated as a knobthat can be selectively rotated to adjust a tool parameter to tune theadjusted OPE 704. Alternatively, for example, one or more of the controlswitches 54 can include one or more buttons that can be depressed totune the adjusted OPE 704.

It should be noted that although the OPE adjuster 25 is illustrated ashaving multiple control switches 54, the OPE adjuster 25 could bedesigned without the control switches 54. In this design, the OPEadjuster 25 can include software that performs the calculation andelectronically provides the adjustments to the components describedherein.

The adjustments made by the control switches 54 can vary pursuant to theteachings provided herein. In one embodiment, one of the controlswitches 54 can cause the wafer stage mover 52 to adjust the tilt of thewafer 28 and the wafer stage 50 about the X axis. As provided herein,movement of the wafer 28 about the X axis adjusts the OPE of the firstexposure apparatus 10A. This feature is discussed in more detail below.

Additionally, the control switches 54 can be used to selectively controland adjust one or more of (i) the lens mover 38 to adjust the sigma,(ii) the aperture mover 44 to adjust the numerical aperture, and/or(iii) the illumination source 32 to adjust the characteristics of theillumination beam. As provided herein, the OPE of the first exposureapparatus 10A can further be changed by adjusting the sigma, adjustingthe numerical aperture, and/or adjusting the characteristics of theillumination beam.

FIG. 2 is a simplified side view of a portion of the wafer 28, a portionof the wafer stage 50, the wafer stage mover 52, the control system 24,and the OPE adjuster 25. In this embodiment, one of the control switches54 is being used to control the wafer stage mover 52 to rotate the waferstage 50 and the wafer 28 an adjustment angle 256 about a tilting axis257 (e.g. the X axis in FIG. 2) relative to the flat Z plane 258. Inthis embodiment, the tilting axis 257 is perpendicular to both the scanaxis 31A and the optical axis 31B (illustrated in FIG. 1). It should benoted that the rotation of the wafer 28 is FIG. 2 is greatly exaggeratedfor clarity.

As provided herein, deliberately induced wafer 28 tilt out of the flat Zplane 258 causes a portion of the images transferred to the wafer 28 tobe out of focus. FIG. 2 illustrates a number of graphs that representaerial images that are being transferred to the wafer 28. Because thewafer 28 is tilted out of the flat Z plane 258, a focused aerial image260 and unfocused aerial images 262 are being transferred to the wafer28. The focused aerial image 260 is transferred to the wafer 28 near thetilting axis 257 because the wafer 28 is properly focused at thislocation. In contrast, the unfocused aerial images 262 are transferredto the wafer 28 away from the tilting axis 257 because the wafer 28 isnot properly focused at these locations. It should be noted that onlythree of the aerial images 260, 262 are shown that make up the compositeaerial image 264. However, every location at the wafer 28 will have adifferent aerial image based upon the level of focus of that portion ofthe wafer 28.

The focused aerial images 260 and unfocused aerial images 262 are summedto provide a composite aerial image 264 that is transferred to the wafer28. As a result thereof, tilting of wafer 28 adds out-of focus images262 to best-focus image 260 to generate the composite aerial image 264.Thus, the amount of tilting can be precisely controlled to preciselycontrol the characteristics of the composite aerial image 264 that isbeing transferred to the wafer 28.

The amount of rotation (tilting) necessary to provide the desiredadjustment to the OPE will vary. In non-exclusive embodiments, theadjustment angle 256 can be between approximately 0.0 to 0.1milliradians.

It should be noted that the sensitivity of the first OPE curve 700 ofthe first exposure apparatus 10A to the tilting of the wafer 28 can bedetermined utilizing lithographic modeling software (e.g. Prolithsoftware sold by KLA-Tencor Corp., located in Austin, Tex.), along withthe other settings of the exposure apparatus 10A and the resist andfeature information. With this design, the first OPE curve for a numberof different adjustment angles 256 can be calculated using thelithographic modeling software.

FIG. 3A is simplified illustration of a first illumination pattern 366Ahaving a first sigma 368A that is generated by the illumination system14 (illustrated in FIG. 1) of the first exposure apparatus 10A(illustrated in FIG. 1), and FIG. 3B is simplified illustration of asecond illumination pattern 366B having a second sigma 368B that is alsogenerated by the illumination system 14 (illustrated in FIG. 1) of thefirst exposure apparatus 10A (illustrated in FIG. 1). In thesenon-exclusive examples, each illumination pattern 366A, 366B includesfour illumination beam portions 370 and the term sigma 368A, 368Brepresents the diameter of the four illumination beam portions 370.Comparing FIGS. 3A and 3B, the second sigma 368B is greater than thefirst sigma 368A.

In this embodiment, one of the control switches 54 (illustrated inFIG. 1) can be precisely controlled to control the lens mover 38(illustrated in FIG. 1) to move the lenses 36 and adjust the sigma 368A,368B of the illumination system 14. It should be noted that thecharacteristics of the aerial pattern (not shown in FIGS. 3A and 3B)that is transferred to the wafer 28 (not shown in FIGS. 3A and 3B), andthe value of the OPE will depend the characteristics of the illuminationsystem 14 including the sigma 368A, 368B of the illumination beamportions 370. Thus, the value of the OPE can be adjusted by adjustingthe sigma 368A, 368B.

It should be noted that the sensitivity of the OPE curve 700 of thefirst exposure apparatus 10A to possible sigma 368A, 368B changes can bedetermined utilizing lithographic modeling software, along with theother settings of the exposure apparatus 10A and the resist and featureinformation.

FIG. 4A illustrates a first pupil fill 472A created by a first numericalaperture 474A of the projection optical assembly 16 (illustrated inFIG. 1) and FIG. 4B illustrates a second pupil fill 472B created by asecond numerical aperture 474B of the projection optical assembly 16. Inthese non-exclusive examples, each pupil fill 472A, 472B includes −1, 0,and +1 diffraction orders locations in the pupil plane. FIGS. 4A and 4Billustrate that the −1 and +1 orders are cut off by the lens numericalaperture. Further, these Figures illustrate that more of the −1 and +1orders are cut off by the smaller second numerical aperture 474B thanthe larger first numerical aperture 474A.

It should be noted that the projection optical assembly 16 forms imagesby recombining the −1, 0, and +1 diffraction orders. Thus, thecharacteristics of the aerial pattern (not shown in FIGS. 4A and 4B)that is transferred to the wafer 28 (not shown in FIGS. 4A and 4B), andthe value of the OPE will depend the numerical aperture and how much ofthe −1 and +1 orders are cut off. Thus, the value of the OPE can beadjusted by adjusting the numerical aperture.

In this embodiment, one of the control switches 54 (illustrated inFIG. 1) can be precisely controlled to control the aperture mover 44(illustrated in FIG. 1) to adjust the size of the aperture 42, thenumerical aperture of the projection optical assembly 16, and the OPE.

It should be noted that the sensitivity of the OPE curve 700 of thefirst exposure apparatus 10A to possible numerical aperture changes canbe determined utilizing lithographic modeling software, along with theother settings of the exposure apparatus 10A and the resist and featureinformation.

Further, the diffraction orders can have a sigma inner 476 and a sigmaouter 478 that each be adjusted to adjust the OPE of the system. Morespecifically, the term annular ratio represents the ratio of the sigmainner 476 to the sigma outer 478 of the diffraction orders. In oneembodiment, one of the control switches 54 (illustrated in FIG. 1) canbe used to precisely adjust the annular ratio by selection of particulardiffracting optical elements and by controlled movement of refractingoptical elements within the illumination apparatus

Moreover, one of the control switches 54 (illustrated in FIG. 1) can beused to precisely adjust a scan synchronization between the reticlestage 46 (illustrated in FIG. 1) and the wafer stage 50 (illustrated inFIG. 1). By adjusting the scan synchronization, different aerial imagesare transferred to the wafer due to mismatched position between thereticle and wafer stages to form an adjusted composite image. The scansynchronization can be adjusted by adjusting the relative positionsbetween the reticle 26 and the wafer 28 throughout the scan.

FIG. 5A illustrates a first laser spectrum 580A generated by theillumination source 32 (illustrated in FIG. 1), a composite aerial image582A, a center wavelength aerial image 584A, a first off-center aerialimage 586A, and a second off-center aerial image 588A. Referring to thefirst laser spectrum 580A, the illumination beam from the illuminationsource 32 has a relatively narrow first wavelength spectrum 590A with afirst center wavelength 592A and a small amount of wavelengths near thefirst center wavelength 592A. In one example, the first centerwavelength 592A is approximately 193.000 nanometers, and the firstwavelength spectrum 590A is approximately plus or minus 0.002 nanometers(e.g. 192.998 to 193.002) relative to the center wavelength 592A.

The lenses in the system all have some chromatic aberration. As a resultthereof, the image transferred to the wafer 28 (illustrated in FIG. 1)degrades slightly off the first center wavelength 592A. Thus, the centerwavelength aerial image 584A transferred by the portion of theillumination beam that is at the first center wavelength 592A is verybright. Alternatively, away from the first center wavelength 592A, thebrightness of the off-center aerial images 586A, 588A decreases. Thus,the center wavelength image is the brightest and unaberrated, while theothers are darker and degraded. For example, the first off-center aerialimage 586A is transferred by the portion of the illumination beam thatis slightly off of the first center wavelength 592A, and the secondoff-center aerial image 588A is transferred by the portion of theillumination beam that is near the edge of the first wavelength spectrum590A.

It should be noted that only three of the aerial images 584A, 586A, 588Aare shown that make up the composite aerial image 582A. However, everylocation along the first wavelength spectrum 590A will have a differentaerial image based upon its wavelength.

The projection optical assembly 16 (illustrated in FIG. 1) projects acomposite of the many different images with the different intensities.Thus, the different aerial images 584A, 586A, 588A combine together tomake the composite aerial image 582A that is transferred to the wafer28.

FIG. 5B illustrates a second laser spectrum 580B that can be generatedby the illumination source 32 (illustrated in FIG. 1), a resultingcomposite aerial image 582B, a center wavelength aerial image 584B, afirst off-center wavelength aerial image 586B, and a second off-centerwavelength aerial image 588B. Referring to the second laser spectrum580B, the illumination beam from the illumination source 32 has a narrowsecond wavelength spectrum 590B with a second center wavelength 592B. Inthis example, the second wavelength spectrum 590B is wider than thefirst wavelength spectrum 590A (illustrated in FIG. 5A), and secondcenter wavelength 592B is still equal to the first center wavelength592A (illustrated in FIG. 5A). For example, the second center wavelength592B can be approximately 193.000 nanometers, and the second wavelengthspectrum 590B can be approximately plus or minus 0.003 nanometers (e.g.192.997 to 193.003).

FIG. 5B also illustrates that the image transferred to the wafer 28(illustrated in FIG. 1) again degrades away from the second centerwavelength 592B. Thus, the center wavelength aerial image 584Btransferred by the portion of the illumination beam that is at thesecond center wavelength 592B is very bright. Alternatively, away fromthe second center wavelength 592B, the brightness of the off-centeraerial images 586B, 588B decreases. Because the second wavelengthspectrum 590B is wider than the first wavelength spectrum 590A, thefirst off-center aerial image 586B and the second off-center aerialimage 588B are more degraded than the corresponding aerial images 586A,586B from FIG. 5A. As a result thereof, the resulting composite aerialimage 582B is different from the composite aerial image 582A from FIG.5A. Thus, the OPE of the system, and the image transferred to the wafercan be varied by varying the wavelength spectrum 590B of theillumination beam from the illumination source 32.

In this embodiment, one of the control switches 54 (illustrated inFIG. 1) can be precisely controlled to control the illumination source32 to widen or narrow the wavelength spectrum 590A, 590B to adjust theOPE.

It should be noted that the sensitivity of the OPE curve 700 of thefirst exposure apparatus 10A to possible bandwidth changes can bedetermined utilizing lithographic modeling software, along with theother settings of the exposure apparatus 10A and the resist and featureinformation.

FIG. 6 is a flow chart that illustrates one embodiment of a processhaving features of the present invention. In this embodiment, at step600, the second OPE curve 702 (illustrated in FIG. 7) of the secondexposure apparatus 10B is provided. The second OPE curve 702 can beobtained during usage of the second exposure apparatus 10B withoutknowledge of the proprietary details of the second exposure apparatus10B.

Next, at step 602, the initial settings (e.g. the tilt of the wafer, thebandwidth of the illumination source, the numerical aperture, the sigma,the annular ratio) of the first exposure apparatus 10A are evaluated.Further, at step 604 the resist and feature information are provided.Next, at step 606, the first OPE curve 700 (FIG. 7) of the firstexposure apparatus 10A is calculated using lithographic modelingsoftware inputted with the initial settings and the resist and featureinformation.

Subsequently, at step 608, the first OPE curve 700 is compared to thesecond OPE curve 702. If the first OPE curve 700 is close enough to thesecond OPE curve 702, the OPE settings match at step 610. Alternatively,if the first OPE curve 700 is not close enough to the second OPE curve702, then one or more of the control switches 54 are manipulated in thelithographic modeling calculation to adjust the OPE of the firstexposure apparatus 10A. Box 614 represents the sensitivites of firstexposure apparatus 10A to the adjustment by the various control switches54.

Next, the adjusted settings (e.g. the tilt of the wafer, the bandwidthof the illumination source, the numerical aperture, the sigma, theannular ratio) of the first exposure apparatus 10A are combined with theresist and feature information to calculate (with lithographic modeling)the adjusted OPE curve 704 (illustrated in FIG. 7). Subsequently, theadjusted OPE curve 704 is compared to the second OPE curve 702. If theadjusted OPE curve 704 is close enough to the second OPE curve 702, theOPE settings match. Alternatively, if there is not a match, one or moreof the control switches 54 are again adjusted and the lithographicmodeling repeated until there is a sufficient enough match.

It should be noted that the matching process can be done without testexposures to the wafer. This reduces the cost of matching the exposureapparatuses 10A, 10B.

Further, it should be noted that the modeling calculations can be eithervia aerial image or in resist, as appropriate.

FIG. 7 is a simplified graph that illustrates the first OPE curve 700(solid line with circles) (sometimes referred to a “initial first OPEcurve”) of the first exposure apparatus 10A (illustrated in FIG. 1), thesecond OPE curve 702 (solid line with squares) of the second exposureapparatus 10B (illustrated in FIG. 1), and the adjusted first OPE curve704 (dashed line) of the first exposure apparatus 10A that was achievedthrough adjustment of one or more of the control switches 44(illustrated in FIG. 1) as described above. As provided herein, one ormore of the control switches 44 can be adjusted until the adjusted OPEcurve 704 closely matches the second OPE curve 702. As a result thereof,exposure apparatuses 10A, 10B (illustrated in FIG. 1) from differentmanufacturers, when using the same reticle 26 (illustrated in FIG. 1),will transfer similar images to a wafer 28 (illustrated in FIG. 1).

FIG. 8 is a simplified graph that includes an original curve 806 (solidline) that represents the OPE difference between the first OPE curve 700(illustrated in FIG. 7) and the second OPE curve 702 (illustrated inFIG. 7), and an adjusted curve 808 (dashed line) that represents the OPEdifference between the adjusted OPE curve 704 (illustrated in FIG. 7)and the second OPE curve 702. FIG. 8 illustrates that the differencebetween the first OPE curve 700 and second OPE curve 702 is much greaterthan the difference between the adjusted OPE curve 704 and the secondOPE curve 702. Thus, one or more of the control switches 44 (illustratedin FIG. 1) can be used to reduce the OPE difference between the exposureapparatuses 10A, 10B (illustrated in FIG. 1).

A photolithography system (an exposure apparatus) according to theembodiments described herein can be built by assembling varioussubsystems, including each element listed in the appended claims, insuch a manner that prescribed mechanical accuracy, electrical accuracy,and optical accuracy are maintained. In order to maintain the variousaccuracies, prior to and following assembly, every optical system isadjusted to achieve its optical accuracy. Similarly, every mechanicalsystem and every electrical system are adjusted to achieve theirrespective mechanical and electrical accuracies. The process ofassembling each subsystem into a photolithography system includesmechanical interfaces, electrical circuit wiring connections and airpressure plumbing connections between each subsystem. Needless to say,there is also a process where each subsystem is assembled prior toassembling a photolithography system from the various subsystems. Once aphotolithography system is assembled using the various subsystems, atotal adjustment is performed to make sure that accuracy is maintainedin the complete photolithography system. Additionally, it is desirableto manufacture an exposure system in a clean room where the temperatureand cleanliness are controlled.

Semiconductor devices can be fabricated using the above describedsystems, by the process shown generally in FIG. 9A. In step 901 thedevice's function and performance characteristics are designed. Next, instep 902, a mask (reticle) having a pattern is designed according to theprevious designing step, and in a parallel step 903 a wafer is made froma silicon material. The mask pattern designed in step 902 is exposedonto the wafer from step 903 in step 904 by a photolithography systemdescribed hereinabove in accordance with the present invention. In step905, the semiconductor device is assembled (including the dicingprocess, bonding process and packaging process), finally, the device isthen inspected in step 906.

FIG. 9B illustrates a detailed flowchart example of the above-mentionedstep 1104 in the case of fabricating semiconductor devices. In FIG. 9B,in step 911 (oxidation step), the wafer surface is oxidized. In step 912(CVD step), an insulation film is formed on the wafer surface. In step913 (electrode formation step), electrodes are formed on the wafer byvapor deposition. In step 914 (ion implantation step), ions areimplanted in the wafer. The above mentioned steps 911-914 form thepreprocessing steps for wafers during wafer processing, and selection ismade at each step according to processing requirements.

At each stage of wafer processing, when the above-mentionedpreprocessing steps have been completed, the following post-processingsteps are implemented. During post-processing, first, in step 915(photoresist formation step), photoresist is applied to a wafer. Next,in step 916 (exposure step), the above-mentioned exposure device is usedto transfer the circuit pattern of a mask (reticle) to a wafer. Then instep 917 (developing step), the exposed wafer is developed, and in step918 (etching step), parts other than residual photoresist (exposedmaterial surface) are removed by etching. In step 919 (photoresistremoval step), unnecessary photoresist remaining after etching isremoved. Multiple circuit patterns are formed by repetition of thesepreprocessing and post-processing steps.

While the designs as herein shown and disclosed in detail is fullycapable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative ofthe presently preferred embodiments of the invention and that nolimitations are intended to the details of construction or design hereinshown other than as described in the appended claims.

1. A method for matching a first OPE curve for a first exposureapparatus used to transfer an image to a wafer to a second OPE curve ofa second exposure apparatus, the method comprising the step of:adjusting a tilt of a wafer stage that retains the wafer to adjust thefirst OPE curve.
 2. The method of claim 1 further comprising the step oflithographic modeling to estimate the first OPE curve of the firstexposure apparatus with the wafer stage at a plurality of alternativeadjustment angles.
 3. The method of claim 1 further comprising the stepof adjusting a numerical aperture of a projection optical assembly ofthe first exposure apparatus to adjust the first OPE curve.
 4. Themethod of claim 1 further comprising the step of adjusting a sigma of anillumination system of the first exposure apparatus to adjust the firstOPE curve.
 5. The method of claim 1 further comprising the step ofadjusting a wavelength spectrum of an illumination system of the firstexposure apparatus to adjust the first OPE curve.
 6. The method of claim1 further comprising the step of adjusting an annular ratio of anillumination system of the first exposure apparatus to adjust the firstOPE curve.
 7. The method of claim 1 further comprising the step ofadjusting a scan synchronization of a reticle stage and the wafer stageof the first exposure apparatus to adjust the first OPE.
 8. The methodof claim 1 further comprising at least two of the steps of: (i)adjusting a numerical aperture of a projection optical assembly of thefirst exposure apparatus to adjust the first OPE curve; (ii) adjusting asigma of an illumination system of the first exposure apparatus toadjust the first OPE curve; (iii) adjusting a wavelength spectrum of anillumination system of the first exposure apparatus to adjust the firstOPE curve; (iv) adjusting an annular ratio of an illumination system ofthe first exposure apparatus to adjust the first OPE curve; and (v)adjusting a scan synchronization of a reticle stage and the wafer stageof the first exposure apparatus to adjust the first OPE.
 9. The methodof claim 1 wherein the step of adjusting a tilt includes adjusting atilt until the first OPE curve approximately matches the second OPEcurve.
 10. A method of making a wafer including the steps of providing asubstrate, matching the first OPE curve to the second OPE curve by themethod of claim 1, and forming an image on the substrate with the firstexposure apparatus.
 11. A method for matching a first OPE curve for afirst exposure apparatus used to transfer an image to a wafer to asecond OPE curve of a second exposure apparatus, the method comprisingthe steps of: retaining the wafer with a wafer stage, the wafer stagebeing tiltable about a first tilting axis; estimating the first OPEcurve with lithographic modeling of the first exposure apparatus withthe wafer stage at a plurality of alternative adjustment angles; andadjusting a tilt of a wafer stage that retains the wafer to adjust thefirst OPE curve until the first OPE curve approximately matches thesecond OPE curve.
 12. The method of claim 11 further comprising the stepof adjusting a numerical aperture of a projection optical assembly ofthe first exposure apparatus to adjust the first OPE curve.
 13. Themethod of claim 11 further comprising the step of adjusting a sigma ofan illumination system of the first exposure apparatus to adjust thefirst OPE curve.
 14. The method of claim 11 further comprising the stepof adjusting a wavelength spectrum of an illumination system of thefirst exposure apparatus to adjust the first OPE curve.
 15. The methodof claim 11 further comprising at least two of the steps of: (i)adjusting a numerical aperture of a projection optical assembly of thefirst exposure apparatus to adjust the first OPE curve; (ii) adjusting asigma of an illumination system of the first exposure apparatus toadjust the first OPE curve; (iii) adjusting a wavelength spectrum of anillumination system of the first exposure apparatus to adjust the firstOPE curve; (iv) adjusting an annular ratio of an illumination system ofthe first exposure apparatus to adjust the first OPE curve; and (v)adjusting a scan synchronization of a reticle stage and the wafer stageof the first exposure apparatus to adjust the first OPE.
 16. A method ofmaking a wafer including the steps of providing a substrate, matchingthe first OPE curve to the second OPE curve by the method of claim 11,and forming an image on the substrate with the first exposure apparatus.17. A first exposure apparatus for transferring an image to a wafer, thefirst exposure apparatus having an initial first OPE curve that isdifferent than a second OPE curve of a second exposure apparatus, thefirst exposure apparatus comprising: a wafer stage that retains thewafer; a wafer stage mover for moving the wafer stage and the waferalong a scan axis and about a tilting axis that is orthogonal to thescan axis; and an OPE adjuster that controls the wafer stage mover torotate the wafer stage and the wafer about the tilting axis to adjustthe initial first OPE curve of the first exposure apparatus.
 18. Thefirst exposure apparatus of claim 17 further comprising a projectionoptical assembly having an adjustable numerical aperture, and whereinthe OPE adjuster controls numerical aperture to adjust the first OPEcurve.
 19. The first exposure apparatus of claim 17 further comprisingan illumination system having a sigma, and wherein the OPE adjustercontrols the sigma to adjust the first OPE curve.
 20. The first exposureapparatus of claim 17 further comprising an illumination system having awavelength spectrum, and wherein the OPE adjuster controls thewavelength spectrum to adjust the first OPE curve.